Digitally Controlled Low-Dropout Regulator with Fast-Transient and Autotuning Algorithms

A digitally controlled low-dropout voltage regulator (LDO) that can perform fast-transient and autotuned voltage is introduced in this paper. Because there are still several arguments regarding the digital implementation on the LDOs, pros and cons of the digital control are first discussed in this paper to illustrate its opportunity in the LDO applications. Following that, the architecture and configuration of the digital scheme are demonstrated. The working principles and design flows of the functional algorithms are also illustrated and then verified by the simulation before the circuit implementation. The proposed LDO was implemented by the 0.18-mu m manufacturing process for the performance test. Experimental results show that the LDO's output voltage V-out can accurately perform the dynamic voltage scaling function at various V-out levels (1/2, 5/9, 2/3, and 5/6 of the input voltage V-DD) from a wide V-DD range (from 1.8 to 0.9 V). The transient time is within 2 mu s and the voltage spikes are within 50 mV when a 1-mu F output capacitor is used. Test of the autotuning algorithm shows that the proposed LDO is able to work at its optimal performance under various uncertain conditions.